This invention relates to a resin composition which comprises a vinylidene chloride copolymer having increased thermal stability and decreased gas permeability and water vapor transmission; and to packaging materials prepared therefrom. In particular, the present invention relates to a vinylidene chloride copolymer which contains about 0.5 -- about 10% by weight of glycidyl methacrylate as an internal heat stabilizer in the polymer chain.
Polyvinylidene chloride resins have been used, in the form of film or sheet or container, for wrapping and packaging foodstuffs, medicines and other materials because of its desirable characteristics, in particular, low gas permeability. However, there are difficulties in forming or molding a resin which has been prepared only from a vinylidene chloride monomer, since the softening point of such a resin is usually so high -- nearly approaching the decomposition point. Therefore, copolymers of vinylidene chloride with one or more copolymerizable monomers, for example vinyl chloride, vinyl acetate, acrylonitrile, methacrylates and allyl esters, have been employed to reduce the difficulties. Generally, additives such as a heat stabilizer, plasticizer and light stabilizer must be added to the copolymer resins to improve the properties thereof. For example, commercially available vinylidene chloride copolymer compositions contain usually about 85 - 95% by weight of vinylidene chloride component and about 15 - 5% by weight of vinyl chloride component and additionally about 2 - 5 PHR* of heat stabilizer (e.g. epoxidated soy bean oil), about 2 - 5 PHR of plasticizer (e.g. dibutyl sebacate or phthalyl butylglycolate) and minor light stabilizer. Of the additives, for example, epoxidated soy bean oil as a heat stabilizer emits an unpleasant oily odor and the odor is carried into articles made from a resin composition containing it. Thus where materials such as foodstuffs and medicines are wrapped by or packaged in film, sheet, bottle, etc. made of such resin composition the unpleasant odor tends to transfer to the contents in a length of time. Further, certain additives have less compatibility with the resin and later may exude gradually to the surface of articles to cause some problem. FNT *Part per hundred parts of resin.